The invention relates to a method for data transmission in a communication network, wherein data frames including metadata and useful data are transmitted via point-to-point connections between a respective transmitter and a receiver according to a communication protocol.
In this case, metadata refer to all data that a data frame includes other than the useful data. Metadata include control and protocol information for the transmission and processing of the data frame, for example addresses of the transmitter and receiver, the type and/or the length of a data frame. Frequently, metadata of a data frame precede the useful data and form the header of the data frame.
At the present time, more and more industrial sectors, particularly the automation and automotive industry and the energy sector, are demanding communication networks that are suitable for all communication services from the field bus level to the management level on the basis of a single standardized protocol. In the industrial sector, communication on the basis of the Ethernet protocol has gained ever more acceptance since the year 2000. Currently, working groups are working on extending Ethernet standards IEEE802.1 and IEEE802.3 (IEEE=Institute of Electrical and Electronics Engineers), which are suitable for communication services in a single convergent “time-sensitive network” (TSN) and allow what is known as quality of service (QoS). Despite this coexistence of different services having different priority in a communication network, it is necessary for minimal transmission times (low latency) and minimal jitter (low jitter) to be guaranteed for high-priority services, e.g. for what is known as control data traffic (CD traffic), for each path between controller and device. The higher the priority of a service, the shorter the transmission time and the lower the jitter need to be in each network node. The influence of lower-priority services on the transmission time and jitter of higher-priority services needs to be minimized in this case. This extensive decoupling is a prerequisite for efficient coexistence of different services having different priority in a communication network.
Currently, what is known as the IEEE802.3br Interspersing Express Traffic (IET) working group is discussing designs for a future Ethernet standard that, in the area of responsibility of the IEEE802.3 standard in a convergent time-sensitive network, minimizes the influence of lower-priority services on the transmission time and jitter of higher-priority services. In particular, high-priority services are intended to be able to interrupt the sending of lower-priority services by means of preemption. To this end, two priority classes are defined. All data frames of the high-priority services are combined in a priority class of what are known as express frames. All other data frames are combined in a priority class of normal data frames (non-express frames). To send an express frame, it is possible for the transmission of a normal data frame to be interrupted.